The first event that made Europeans aware of Islam's coming important place in their lives was the caliph 'Umar ibn al-Khattab's capture of Jerusalem (638). This caused Europe to realize for the first time that Islam was spreading and approaching its own borders. The main reason for the Crusades, launched four centuries later, was to take Jerusalem back from the Muslims. But the Crusaders who set out for this purpose gained something else, for the contact they made with the Muslim world was the first step toward Europe's rebirth. Dominated by darkness, conflict, war, and despotism, Europe encountered the Islamic world's advanced civilization and saw that its inhabitants were both highly prosperous and civilized, as well as quite advanced in the fields of medicine, astronomy, and mathematics as in their social lives. They also saw that values rarely found in Europe at that time (e.g., pluralism, tolerance, understanding, compassion, and self-sacrifice) were aspects of the high morality expressed by Muslims, who were aware of their religious responsibilities